The overall objective of this research proposal is to examine neutrophil function and signaling in Polynesian children with severe or recurrent infections. Remarkably, fifty percent of all children admitted for bacterial infections at the primary pediatric hospital in Hawaii are of Polynesia ethnicity. We propose to examine neutrophil respiratory burst activity, phagocytosis, chemotaxis, and the expression of the high affinity receptor for IgG (FcgammaRI) in these children. A novel disorder of neutrophil actin polymerization in a Tongan child and his family in Los Angeles, characterized by impaired neutrophil chemotaxis and the increased expression of an actin binding protein identified as lymphocyte specific protein 1 (LSP1) suggests a mechanism for the increase in infections. We propose to examine both functional and biochemical characteristics of neutrophils in Polynesian children with infections to test the hypothesis that defects in neutrophil function and cellular signaling pathways result in their increased susceptibility to infection. The following specific aims will be performed. Aim 1: Investigate neutrophil chemotaxis, phagocytosis, superoxide production, and neutrophil FcgammaRI expression in Polynesian children who prevent with severe and/or recurrent bacterial infections. Aim 2: Determine the activation of the small GTPase proteins Rac and Cdc42, the activation of p38 mitogen activated protein kinase (p38 MAPK) and mitogen activated protein kinase activated protein kinase 2 (MAPKAP K2), and the protein level and phosphorylation status of the actin-binding protein LSP1 in neutrophils of Polynesia children with increased infections and impaired chemotaxis. Aim 3: Investigate the involvement of LSP1 in F c receptor- mediated respiratory burst and cytoskeletal rearrangement in neutrophils and neutrophil-like or monocyte-like cell lines by protein immunoprecipitation and the measurement of Rac, Cdc42, phosphatidylinositol 3-kinase, p38MAPK, MAPKAP K2 and protein kinase C activation. Aim 4: Over-express LSP1 in neutrophil-like myeloid cell lines to determine its functional and biochemical effect on cytoskeleton organization, cell motility and FcgammaRI signal transduction. The finding of neutrophil dysfunction in Polynesia children with increased bacterial infections, along with associated biochemical abnormalities, will lead to improved diagnosis and potential treatment of these children. The use of immune modulators such as gamma-interferon, based on its up-regulation of FcgammaRI expression and enhancement of neutrophil function, may improve the clinical outcome of those with the severest infections.